Certain types of prior personal computer systems each include a microprocessor (also referred to as a central processing unit or CPU) that is coupled to several types of storage systems--namely, a read only memory ("ROM"), a random access memory ("RAM") or dynamic random access memory ("DRAM"), a hard (i.e., fixed) disk drive for mass storage, and a floppy disk drive or drives for storage on removable magnetic floppy disks. The floppy disks are also referred to as diskettes.
A relatively new mass storage device is a flash memory card. One prior art flash memory card includes flash electrically erasable programmable read only memories ("flash EEPROMs") and an electrical connector as part of a plastic package that is smaller than a 3.5 inch floppy disk. The flash memory card can be connected to a personal computer via the electrical connector.
The flash EEPROM is a nonvolatile memory that can be programmed by the user. Once programmed, the flash EEPROM retains its data until erased. Electrical erasure of the flash EEPROM erases the entire contents of the memory of the device in one relatively rapid operation. The flash EEPROM may then be reprogrammed.
That prior art flash memory card allows for the storage of data files and application programs on the purely solid-state medium of flash EEPROMs. System resident flash filing systems permit the prior art flash memory card to function as if it were a physical disk drive. The prior flash memory card in conjunction with a flash filing system provides an alternative to both a fixed hard disk and a floppy disk in a Disk Operating System ("DOS") compatible portable personal computer ("PC").
The storage of user application software on a prior art flash memory card substantially reduces the relatively slow prior art disk-DRAM download process. That prior art flash memory card can be read from faster than certain prior art hard disk drives. That prior art flash memory card generally uses less power than certain prior art hard disk drives. That prior art flash memory card is also smaller and lighter than certain prior art hard disk drives.
Prior art personal computers typically have a redundant memory structure--i.e., there is a DRAM for storage of applications and data to be executed plus a hard disk or a floppy disk for mass storage. Applications and data need to be loaded into the DRAM.
The prior art flash memory card, however, has a read access time and a command register microprocessor write interface that permits an "execute-in-place" architecture. This configuration eliminates the need for a DRAM. Thus, redundancy associated with having both a DRAM and disk drive is eliminated.
Certain prior art flash memory cards can be transported from personal computer to personal computer. Moreover, the flash EEPROMs of certain flash memory cards are nonvolatile and thus do not require a battery back-up.
One type of flash EEPROM used in a prior art flash memory card has a standby mode that disables most of the flash EEPROM circuitry and reduces device power consumption. This flash EEPROM also has an active mode. The active mode requires increased power consumption. The active mode is used when the flash EEPROM is being written to, read from, or erased.
One disadvantage, however, of certain flash memory cards is that a microprocessor has to step through relatively complex erasure or programming software routines in order to erase or program the flash memory card.
Another disadvantage of certain flash memory cards is that even when the flash EEPROMs making up the card are in the standby mode, the flash memory card still consumes a significant amount of power. The amount of power consumed by a flash memory card with flash EEPROMs in the standby mode is especially noticeable when the flash memory card is used in conjunction with a battery-powered laptop personal computer. In order to extend battery life, power consumption must be kept to a minimum for a battery-powered laptop personal computer.
Recently, improvements have been made in flash EEPROMs. Memory capacity has been increased. In addition, one type of prior art flash EEPROM includes a write state machine on the flash EEPROM chip.
The write state machine comprises circuitry that automatically steps the prior art flash EPROM through a multistep program or erasure sequence upon receiving an initiating command from a microprocessor. The prior art flash EPROM includes a ready/busy output pin that indicates whether the write state machine is ready to accept a command or whether the write state machine is currently busy programming or erasing the flash EEPROM.
That type of prior art flash EEPROM also includes a power down mode that can be initiated by applying a logical signal to a power down pin. In the power down mode, the flash EEPROM consumes less power than in the standby mode.